1. Field of the Invention
The present invention relates generally to ultra-wideband communication systems, and, in particular, to a convolutional code for use in a communication system.
2. Description of the Related Art
In general, in the descriptions that follow, we will italicize the first occurrence of each special term of art, which should be familiar to those skilled in the art of ultra-wideband (“UWB”) communication systems. In addition, when we first introduce a term that we believe to be new or that we will use in a context that we believe to be new, we will bold the term and provide the definition that we intend to apply to that term. In addition, throughout this description, we will sometimes use the terms assert and negate when referring to the rendering of a signal, signal flag, status bit, or similar apparatus into its logically true or logically false state, respectively, and the term toggle to indicate the logical inversion of a signal from one logical state to the other. Alternatively, we may refer to the mutually exclusive boolean states as logic—0 and logic—1. Of course, as is well know, consistent system operation can be obtained by reversing the logic sense of all such signals, such that signals described herein as logically true become logically false and vice versa. Furthermore, it is of no relevance in such systems which specific voltage levels are selected to represent each of the logic states.
Generally, in an ultra-wideband (“UWB”) communication system, a series of special processing steps are performed by a UWB transmitter to prepare payload data for transmission via a packet-based UWB channel. Upon reception, a corresponding series of reversing steps are performed by a UWB receiver to recover the data payload. Details of both series of processing steps are fully described in IEEE Standards 802.15.4 (“802.15.4”), 802.15.4a (“802.15.4a”), and 802.15.4f (“802.15.4f”) copies of which are submitted herewith and which are expressly incorporated herein in their entirety by reference. As is known, these Standards describe required functions of both the transmit and receive portions of the system, but specific implementation details only of the transmit portion of the system, leaving to implementers the choice of how to implement the receive portion.
One of us, Michael McLaughlin, has developed certain improvements for use in UWB communication systems, which improvements are fully described in the following pending applications or issued patents, all of which are expressly incorporated herein in their entirety:
“A Method and Apparatus for Generating Codewords”, U.S. Pat. No. 7,787,544, issued 31 Jul. 2010 (“Related Patent #1”);
“A Method and Apparatus for Generating Codewords”, application Ser. No. 11/309,222, filed 13 Jul. 2006, now abandoned (“Related Application #1”);
“A Method and Apparatus for Transmitting and Receiving Convolutionally Coded Data”, U.S. Pat. No. 7,636,397, issued 22 Dec. 2009 (“Related Patent #1”); and
“A Method and Apparatus for Transmitting and Receiving Convolutionally Coded Data”, application Ser. No. 12/590,124, filed 3 Nov. 2009 (“Related Application #2”).
Some of us have participated in the development of certain improvements in a receiver for use in UWB communication systems, which improvements are fully described in the following pending applications, all of which are expressly incorporated herein in their entirety:
“A Receiver for Use in an Ultra-Wideband Communication System”, application Ser. No. 12/885,517, filed 19 Sep. 2010 (“Related Application #3”).
“An Adaptive Ternary A/D Converter for Use in an Ultra-Wideband Communication System”, application Ser. No. 13/033,098, filed 23 Feb. 2011 (“Related Application #4”).
As described in U.S. Pat. No. 7,636,397 and Related Application #2, the coded bits of a convolutional code are often transmitted using Binary Phase Shift Keying (“BPSK”). The coded bits of a convolutional code may also be transmitted using On-Off Keying (“OOK”). In OOK modulation, digital data may, for example, be represented as a logic one level if a carrier wave is present and represented as a logic zero level if a carrier wave is not present. The data is typically examined over a pre-determined period of time.
As is known, a Viterbi decoder may be included in the receiver of the system. Depending on the complexity of the Viterbi decoder, received channel symbols may be quantized to one bit of precision (“hard decision”) or more than one bit of precision (“soft decision”). As is known, a Viterbi decoder that uses a soft decision algorithm typically performs better than a Viterbi decoder that uses a hard decision algorithm.
We submit that what is needed is an improved method and apparatus for transmitting and receiving convolutional code for use in a communication system. For example, the communication system may operate as described in 802.15.4f. In particular, we submit that such a method and apparatus should provide performance generally comparable to the best prior art techniques while requiring less circuitry and consuming less power than known implementations of such prior art techniques.